(define-syntax (make-info-proc x r t)
    ;; like list-ref but returns #f instead of failing
    ;; and returns original item on non-lists if idx == 0
    ;; (list-ref-maybe '(mass a b c) 3) ==> c
    ;; (list-ref-maybe '(mass a b c) 4) ==> #f
    ;; (list-ref-maybe 'mass 0) ==> mass
    ;; (list-ref-maybe 'mass 2) ==> #f
    (define (list-ref-maybe lst idx)
      (if (list? lst)  
          (and (> (length lst) idx) (list-ref lst idx))
          (and (= idx 0) lst)))

    (let* ([spec (cadr x)]
           [getter-prefix (caddr x)]
           [setter-prefix (cadddr x)])
      `(lambda (body)
         (list ,@(map (lambda (item)
                        (let* ([field (list-ref-maybe item 0)]
                               [get-conv (list-ref-maybe item 1)]
                               [set-conv (list-ref-maybe item 2)]
                               [getter (list-ref-maybe item 3)]
                               [setter (list-ref-maybe item 4)]
                               [getter-proc-name (or getter 
                                                     (string->symbol (conc getter-prefix field)))]
                               [getter-proc-call (list getter-proc-name 'body)])
                          `(list (quote ,field)
                                 ;; call getter with body as parameter
                                 ,(if get-conv
                                      `(,get-conv ,getter-proc-call)
                                      getter-proc-call))))
                      spec)))))